Starter circuit for three-electrode gaseous discharge device



Sept. 24, 1968 c. H. MICHELSEN 3,4039293 STARTER CIRCUIT FOR THREE-ELECTRODE GASEOUS DISCHARGE DEVICE Filed July 29, 1966 was 3% BYmMwf- United States Patent O 3,403,293 STARTER CIRCUIT FOR THREE-ELECTRODE GASEOUS DISCHARGE DEVICE Claus Henry Michelsen, Tustin, Calif., assignor to Philco- Ford Corporation, a corporation of Delaware Filed July 29, 1966, Ser. No. 568,915 5 Claims. (Cl. 315-168) ABSTRACT OF THE DISCLOSURE Starter circuit for three-electrode gaseous discharge device using pulse source and transformer to supply high starting voltage between starting electrode and cathode, with additional transformer winding connected to raise voltage of anode during starting period to prevent starting electrode to anode arc.

The present invention relates to control circuits for gaseous discharge devices and more particularly `to means for and a method of starting a three electrode gaseous discharge device.

Gaseous discharge devices such as high pressure arc lamps require a higher voltage to initiate conduction than to sustain conduction. This initial higher voltage is necessary to initiate ionization of the gas in the device. Once ionization has been achieved, a smaller voltage is sufcient to sustain the ionization of the gas and hence conduction of the device.

It is well known that the magnitude of the voltage required to initiate ionization in the vicinity of the cathode and hence initiate conduction of gaseous discharge device may be reduced by providing a starter electrode positioned in proximity to the cathode and by supplying the starting or ionizing potential between this starting electrode and the cathode, Although the starter electrode is positioned closer to the cathode than the anode, an arc, known as a long arc, often develops between the anode and the starting electrode. The formation of the long arc lowers the potential of the starting electrode to the point that no arc is formed between the starting electrode and the cathode. Generally the long arc is not of sufficient intensity to cause suicient ionization of the gas in the device to initiate conduction. This can be a serious disadvantage if the gaseous discharge device is used in a control or telemetry system.

An object of the present invention is to provide a circuit which will insure conduction in a gaseous discharge device on each starting impulse.

Another object of the present invention is to provide a circuit which will eliminate the long arc which often exists when starting a gaseous discharge device.

A further object of the present invention is to provide a circuit which does not require electro-mechanical switching devices for isolating the starter circuit during starting pulses.

These objects are achieved and the disadvantages of prior art starter circuits are overcome by providing means for minimizing the potential difference between the anode and the starter electrodes during starting pulses, preferably by increasing the potential of the anode upon the application of a starting pulse to the starting electrode.

The single gure of the drawing illustrates a circuit diagram in accordance with one embodiment of the present invention.

The gaseous discharge device control circuit illustrated in the drawing comprises a gaseous discharge device 8 having a cathode 13, an anode 12 and a starting electrode 14. Device 8 may comprise a high pressure arc lamp which produces a light output which is proportional to arc current. A rst serially connected circuit comprising a driver supply 20 and a diode 2 is connected between the anode 12 and cathode 13 of device 8. The driver source 20 supplies the main operating current for device 8. If the circuit is to be employed as a telemetry transmitter, source 20 may comprise a source of timewidth modulated current pulses.

A second serially connected circuit comprising a DC boost source 5, a resistor 4, and a diode 3 is also connected in parallel with the gaseous discharge device 8. The DC boost source voltage is sutlicient to maintain minimum conduction of gaseous discharge device 8 in the absence of a signal from source 20. Diodes 2 and 3 may be high voltage avalanche rectifiers.

One terminal of a pulse starting source 6 is connected t0 the cathode 13 of device 8 and to one terminal of the primary Winding 9 of a step-up transformer 7. The other terminal of primary winding 9 is connected to the other terminal of the pulse starting source 6 by way of momentary contact switch 15. The transformer 7 has two secondary windings 10 and 11. The secondary winding 10 is connected between the starting electrode 14 and the cathode 13. The secondary winding 11 is connected between the anode 12 and the cathode 13. The secondary windings 10 and 11 are similarly wound and are constructed of a pro-per number of turns so that a positive Voltage appears at the anode 12 and a positive voltage many times greater than the anode voltage appears at the starter electrode 14 when a starting pulse is supplied to the primary winding 9. Preferably the anode voltage should be approximately 10% of the starter electrode voltage.

Diodes 2 and 3 have their respective cathodes connected to the anode 12 so that they are back biased and hence non-conducting when a high positive potential is supplied to anode 12 by the winding 11. Diodes 2 and 3 will thereby isolate sources 20 and 5, respectively, from the starting circuit. As a result of the isolation achieved by diodes 2 and 3, electro-mechanical isolation devices are not needed and the reliability of the circuit is thereby increased.

When the start generator 6 is connected to the transformer 7 by the closure of switch 15, a voltage is induced in secondary windings 10 and 11. Since the windings 10 and 11 are similarly wound, positive voltages are developed at the anode 12 and the starter electrode 14. Since the voltage developed at the anode 12 raises the anode potential, preferably by approximately 10% of starter electrode voltage, the potential difference existing between electrodes 12 and 14 is not suicient to produce an arc between electrodes 12'and 14. Therefore, an arc will strike between the cathode 13 and the starter electrode 14 and the gaseous discharge device 8 will ionize sufficiently to initiate conduction. Once conduction has been initiated by the starter electrode 14, the DC boost source voltage is of sufficient magnitude to maintain conduction of the gaseous discharge device 8 at an intensity determined by the magnitude of the limiting resistor 4. Usually conduction will be maintained at the minimum level which will insure continuous conduction of gaseous discharge device 8. Conduction through gaseous discharge device 8 is increased, and the light output of gaseous discharge device 8 correspondingly increased, by current supplied to gaseous discharge device 8 by source 20. As noted above, in one embodiment of the invention timewidth modulated current pulses are supplied by source 20 to produce correspondingly time-width modulated pulses of intense light from gaseous discharge device 8. The provision of the boost source 5 makes it unnecessary to restart gaseous discharge device 8 on each pulse from driver source 20 and hence increases the speed of response of gaseous discharge device 8 to the `driver source pulses.

While only a single embodiment of the present invention has been illustrated and described, it is apparent that modifications and changes may be made without departing from the true scope of the present invention as defined in the appended claims.

What I claim is:

1. In a starter circuit for a three electrode gaseous discharge device: a gaseous discharge device having an anode, a cathode, and a starter electrode, first means coupling a source of direct current in parallel with said anode and said cathode, second means coupling a driver source in parallel with said anode and said cathode, a transformer having a primary winding connected to pulsing means and a Iirst secondary winding connected to said cathode and said starter electrode, and means for preventing the formation of an arc between said anode and said starter electrode.

2. The circuit of claim 1 in which said means for preventing the formation of an arc comprises a second secondary winding on said transformer, said second secondary winding being connected between said cathode and said anode and poled to change the potential of said anode in the same direction as the change in potential on said starter electrode in response to pulses supplied to said primary Winding.

3. The ycircuit of claim 2 in which said second means of claim 1 includes a diode having its cathode connected to said anode and in which said lirst means of claim 1 includes a resistor and a second diode serially connected between the positive terminal of said source of direct current and said anode.

4. The circuit of claim 3 in which said source of direct current is just sufficient to maintain said device in conduction after conduction has been initiated by said pulsing means.

5. The circuit of claim 4 in which said driver source supplies periodic pulses of current to said device, said pulses having a polarity that increases the conduction of said device to produce modulated pulses of intense light from said device.

References Cited UNITED STATES PATENTS 2,235,385 3/1941 Rava 315-171 X 2,562,887 8/1951 Beese 315-176 X 2,777,973 1/1957 Steele et al. 315-176 X 2,834,917 5/1958 Moignet 315-176 X 3,087,065 4/1963 Mutschler 315-176 X 3,280,366 10/1966 Ahmed 315-171 X 3,334,270 8/1967 Nuckolls 315-171 X r JAMES W. LAWRENCE, Primary Examiner. J

C. R. CAMPBELL, Assistant Examiner. 

